1. Field of the Invention
The present invention relates to a plasma processing apparatus.
2. Description of the Related Art
A plasma processing apparatus is conventionally employed in the process of manufacturing semiconductor devices. Such a plasma processing apparatus is provided with an upper electrode and a lower electrode facing opposite each other inside a processing chamber. In a plasma processing apparatus adopting this structure, the processing gas induced into the processing chamber is raised to plasma by applying high-frequency power to the upper electrode and the lower electrode so that plasma processing may be performed on a workpiece placed on the lower electrode.
In the apparatus in the prior art described above, plasma is diffused inside the processing chamber during the process. This causes deposition attributable to the plasma to become adhered to the inner wall surfaces of the processing chamber and the surfaces of the various members exposed inside the processing chamber. In addition, when such deposition is accumulated to a certain degree, the deposition begins to peel off to become loose particles which will contaminate the workpiece. As a result, the apparatus in the prior art necessitates frequent cleaning to remove the deposits, which in turn lowers the throughput.
Openings such as a gas discharge port through which the gas inside the processing chamber is discharged and a detection port through which plasma light is detected are normally formed at an inner wall of the processing chamber. The presence of these openings poses a problem in that plasma is generated in a nonuniform manner and consequently, uniform processing cannot be performed on the workpiece.
Furthermore, in the prior art, the distance between the upper electrode and the lower electrode is adjusted in order to optimize the plasma in conformance to the particulars of a given process. However, there is a problem with an apparatus adopting the structure in the prior art in that if the distance between the electrodes is changed, the conductance at the gas discharge path also changes, to result in plasma becoming unstable.
An object of the present invention, which has been completed by addressing the problems of the prior art discussed above, is to provide a new and improved plasma processing apparatus capable of eliminating the problems discussed above and other problems.
In order to achieve the object described above, the present invention provides a plasma processing apparatus having a first electrode and a second electrode facing opposite each other inside a processing chamber into which a processing gas is induced with plasma being generated between the first electrode and the second electrode by applying high-frequency power in order to perform a plasma process on a workpiece placed on the second electrode. The plasma processing apparatus is provided with a first ring-shaped body that covers the circumferential edge of the first electrode, a cylindrical body that is provided around the first ring-shaped body to surround the workpiece during a plasma process and a second ring-shaped body that is provided around the second electrode and is positioned inside the cylindrical body during the plasma process, with a gas discharge path formed between the cylindrical body and the second ring-shaped body during the plasma process.
According to the present invention, the plasma is prevented from becoming diffused onto the processing chamber inner walls by the cylindrical body and the second ring-shaped body during the plasma process. As a result, almost no deposits adhere to the processing chamber inner wall surfaces. In addition, the first and second ring-shaped bodies and the cylindrical body are exposed to the plasma and become heated during the process. Thus, even though the first ring-shaped body, the second ring-shaped body and the cylindrical body are exposed to the plasma, deposits do not adhere to them readily. Consequently, the intervals between maintenance required to remove deposits can be lengthened to improve productivity.
In addition, during the plasma process, it is desirable to set the distance between the cylindrical body and the second ring-shaped body so as to ensure that the conductance value of the gas within the gas discharge path is larger than the conductance value of the gas inside the space where plasma is generated. By ensuring this, the gas flow is deterred to a certain extent in the gas discharge path to rectify the flow of the gas inside the space. As a result, a uniform plasma flow is achieved to induce the plasma to the workpiece in a uniform manner. Thus, the workpiece can be uniformly processed.